Time: 14. January 2020
Place: QISS HKU 2020 Workshop, Hong Kong
Title: Definite vs superposed causal orders and quantum gravity
We will discuss the realisations of the quantum switch using 4 and 3 gates in classical spacetimes with fixed causal orders, and a realisation of a gravitational switch with only 2 gates that features superpositions of different gravitational field configurations and their respective causal orders. An observable will be constructed that can distinguish between the quantum switch in classical spacetime, and the gravitational switch in superposed spacetimes. Using this observable, we will argue that the current experimental implementations of the quantum switch do not feature superpositions of causal orders, and that these superpositions can only occur in the case of a gravitational switch. Finally, we will shortly reflect on the limits of the modern relational approach to physics. Based on arXiv:1905.09682.